Justification:
Although this species may have a restricted range, it is not believed to approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

This species winters on tropical islands in most oceans, excluding the eastern Atlantic. It winters at sea in the same area, just ranging north of the Tropic of Cancer, and just south of the Tropic of Capricorn (del Hoyo et al. 1992).

The global population is estimated to number > c.1,000,000 individuals (del Hoyo et al. 1992), while national population sizes have been estimated at < c.100 breeding pairs and < c.50 individuals on migration in Taiwan and < c.100 breeding pairs and < c.50 individuals on migration in Japan (Brazil 2009).

Trend Justification: The population is suspected to be in decline owing to habitat loss, predation by invasive species and unsustainable levels of exploitation.

This species is strictly marine and largely pelagic. It feeds mainly on flying-fish and squid with a mean prey length of 8.8 cm. Prey are caught by plunge-diving, but flying fish are also taken in flight especially when chased by underwater predators. It often rests on boats using them as vantage points. Breeding is not seasonal in most of its range. Individuals form large colonies, nesting and roosting mainly in trees or on islets with abundant vegetation (del Hoyo et al. 1992).